Electrical heating unit and pad



Sept. 9, 1941. A. w. BULL EIAL ELECTRICAL HEATING UNIT AND PAD Filed April 24, 1940 Patented Sept. 9, 1941 2,255,376 A. ELECTRICAL HEATING UNIT AND PAD Arthur W. Bull, Grosse Pointe,. and Glenn G.

Havens, Detroit, Mich., States Rubber Company,

assignors to United New York, N. Y., a

corporation of New Jersey Application April 24, 1940, Serial No. 331,338

11 Claims.

This invention relates to an electrical heating unit and pad, and more particularly to a portable and flexible electrical heating unit, and pad embodying one or more of these units in its construction.

In the manufacture of heating pads it has heretofore been the general practice to incorporate in heating pads elements in the form of metallic wires having the desired electrical resistance for heating the pads.

We have found that an electrically conducting rubber composition, or the dried residue of an electrically conducting rubber cement may be utilized when properly supported as the heating element for pads of this type. A layer or coating of electrically conducting rubber may be applied to a woven fabric or similar supporting means, as a medium for retaining the conducting rubber in the form of a sheet having heating properties. Because of the flexibility of a heating element of this description, danger of forming interruptions in the current due to breakage of the conductor is largely eliminated. The heating unit and pad containing such unit each lends itself more readily to applications of severe usage, particularly when subjected to considerable flexing.

It is, therefore, among the objects of our in-' vention to provide a heating pad which may be subjected to considerable flexing without danger of causing a break in the heating element itself; to provide a heating element which is capable of producing heat uniformly throughout its area; and to provide a heating unit which may be manufactured efliciently and economically for use in various fields where the production of heat over an extended area is desired. These and other objects of the invention will appear more fully in the following detailed description when considered in connection with the accompanying drawing, in which:

Fig. 1 is a perspective view, partly broken away,

, illustrating a pad embodiment of our invention,

and

Fig. 2 is a transverse view, in section, taken along lines 2-2 of Fig. 1, and illustrating diagrammatically the component parts of the heating pad.

With reference to the drawing, we show a heating pad I in which is contained electrically heating elements 2 and 3. These elements are formed by treating fabric so as to render the fabric electrically conducting. We have found that the fabric may be coated with an electrically onducting layer of rubber composition. This layer may be applied to the fabric by dipping, painting, or spraying it with a particular form of rubber cement and thereafter drying or vulcanizing to deposit a rubber composition residue. Essentially, such a rubber composition embodies acetylene carbon black or other electrically conducting blacks in the order of approximately parts to parts of rubber. An example of an electrically conducting cement is as follows:

Rubber 100. Conducting carbon black 85. ZnO 15. Antioxidant .75 Accelerator 2.00 Deodorant .10 Softener 7.00 Vulcanizing agent .75 Gasoline 1500.

By a proper application of the conducting cement to a supporting fabric, it is possible to obtain the desired degree of conductivity on the finished fabric. The fabric base serves merely as a supporting agent for the conducting cement and may be formed of any flexible electrically non-conducting material. We have found that square woven cotton fabric is effective as a supporting medium. However, other materials, such as asbestos, rayon, or woven glass may be used as a substitute. An electrically non-conducting sheet of rubber may also be used as a flexible base upon which the conducting cement is applied, or a conducting rubber composition may serve as both the conducting medium and as the base.

Having provided a fabric sheet embodying the vulcanized conducting cement, we complete the formation of a conducting element such as the element 2 by attaching conducting wires 4 and 5 of different polarity at the marginal portions of opposite edges of the treated fabric 2 to hereby form what is herein called a heating unit. These wires are placed at two sides only of the treated fabric. In order to secure the wires in place, marginal portions 6 and I of the treated fabric are folded around the wires 4 and 5, respectively, and adhered together with the principal body of the fabric. A heating unit thus formed may be placed in a press and vulcanized, thus insuring a. positive retention of the wires 4 and 5 in their respective positions. Preferably, the wires 4 and 5 should be substantially flexible as, for example, braided copper wire. Also, the wires should be tinned so as to prevent any deteriorating defects in size than the heating elements 2 and 3 and 7 between the copper and the vulcanizedrubber composition.

By employing a sheet of flexible material carrying sufficient electrically conducting carbon black to impart current conducting and heating properties to this sheet, and by securing electric conductor wires along two opposite edges of the sheet as above described, a heating unit is secured in which current will be conducted uniformly across the sheet from one wire to the other throughout the length of the sheet to heat all portions of the sheet uniformly, and if desired at a moderately high temperature which is not sufficient to cause a fire hazard or burn a person upon touching the same. The heating element 3, incorporating oppositely disposed wires 8 and 9, to form a second heating unit, may be prepared in substantially the same manner as that described in connection with the heating element '2. i

While it is understood that one heating unit may be employed eficiently to produce a heatin pad, two or more units may be incorporated in the pad, principally for the purpose of permitting variation in the degree of heat to be generated by the pad. In addition, in order to obtain a still further variation, the heating elements may be treated with the conducting cement to provide different degrees of electrical resistivity. For example, the heating element 2 may be treated to provide a resistivity in the order of 309 ohms and the heating element 3 may be treated to provide a resistivity of 500 ohms. By such an arrangement it is possible through a variable switch to choose the desired resistivity which may be 300 ohms, 500 ohms, or a parallel connection of the two elements giving 187 ohms. It is also possible, although usually not desirable, to arrange the wiring so the two elements may be connected in series to give a resistance of 800 ohms.

As shown in Fig. 2, the wires and 8 may be joined together with wire id for the purpose of forming an electrical connection to these wires. A conventional bi-metal thermostat ii may be interposed between the wire it in close proximity to the heating elements for the purpose of breaking the circuit in the event the heating pad reaches a predetermined temperature.

The wires 5 and 9 are connected by wires i2 and I3 respectively to a conventional switch it provided for the purpose of selectively obtaining the desired degree of heat from the heating pad. The switch l4 as indicated in Fig. 1, may be marked with such references as 1, or 3 or off, low, medium, and high, in order to designate the efiect desired. The wires'ic, l2, and I 3, as shown in Fig. 2, may be grouped together to form a line l5 extending from the heating pad to the switch 14. From the switch It a continuation line l6 engages with a conventional adapter I! for complementary engagement with a conventional electrical outlet fixture.

In order to insulate the heating elements 2 and 3, we provide separation layers l8, l9, and 20. Preferably these layers are formed of woven cotton fabric or other textile material or as in the case of the elements, they may be formed of woven asbestos or glass. These layers are preferably treated with a rubber composition by dipping, spraying, or brushing a rubber cement on to the surface of the fabric. In this case, however, the rubber cementis of conventional composition, that is, it is considered to have good insulating characteristics. The separation layers l8, l9, and 20 of insulating material are larger after assembly with the heating elements, their marginal portions are joined together to form a common assembly. These layers i8, i9, and 20 may be vulcanized in a preceding operation and their edges cemented together to encase completely the heating elements 2 and 3. Preferably, however, the common assembly comprising the separation layers of insulating material assembled with the heating elements 2 and 3 are joined together in their unvulcanized state and the entire assembly vulcanized in one operation. The entire assembly as thus described, may be covered with the fabric 2! in order to make a neat appearance of the heating pad, and in order to provide a pleasant texture to the outer surface of the heating pad.

While we have shown and described a preferred embodiment of our invention, it is to be understood that the pad is susceptible of various modifications, and that the electrical heating unit such as formed of the parts 2, l and 5 or the parts 3, 8 and 9 is well adapted for use in other fields where the application of heat over an extended surface is desired.

Havingthus shown and described our invention, what we claim and desire to protect by Letters Patent is:

1. A portable electrical heating unit that is sumciently flexible to conform to different shaped objects to be heated, comprising a fabric sheet provided with a plastic composition containing rubber and electrically conducting carbon black in amount sufficient to impart current conducting and heating properties to the fabric, and electric conductor wires secured to spaced portions of the current conducting fabric along the fabric in parallel relation to each other so that current will be conducted from one wire to the other uniformly across the area ofthe fabric lying be; tween these parallel wires to heat this area uniformly.

2. A portable electrical heating unit that is suficiently flexible to conform to different shaped objects to be heated, comprising a flexible nonmetallicsheet carrying a plastic composition containing rubber and electrically conducting carbon black in amount sufiicient to impart current conducting and heating properties to the sheet, and electric conductor wires secured to spaced portions of the current conducting sheet along the sheet in parallel relation to each other so that current will be conducted from one wire to the other uniformly across the area of the sheet lying between these parallel wires to heat this area uniformly.

tric conductor wires secured along the sheet in spaced parallel relation to each other so that current will be conducted uniformly across the area ofthe sheet lying between these parallel wires to heat this area uniformly.

4. A portable electrical heating unit that is sufiiciently flexible to conform to different shaped objects to be heated, comprising a fabric sheet carrying a coating of plastic containing rubber and electrically conducting carbon black in amount suflicient to impart current conducting and heating properties to the coating of the fabthe area of the fabric in spaced relation to each ric, and electric conductor wires secured to spaced portions of the coated fabric along the fabric in parallel relation to each other so that current will be conducted from one wire to the other across lying between these parallel wires to heat this area uniformly.

5. A portable electrical heating unit that is sufllciently flexible to conform to different shaped objects to be heated, comprising a sheet of flexible material provided with an electrically conducting layer of rubber composition to impart current conducting and heating properties to the sheet, and electric conductor wires secured along the sheet in spaced parallel relation to each other so that current will be conducted uniformly across the area of the sheet lying between these parallel wires to heat this area uniformly.

6. A portable electrical heating unit that is suiflclently flexible to conform to different shaped objects to be heated, comprising a sheet of flexible material provided with an electrically conductive rubber composition to impart current conducting and heating properties to the sheet, and electric conductor wires secured along the sheet in spaced relation to each other so that current will be conducted across the area of the sheet lying between these wires to heat this area. v

'7. A readllyiportable and flexible heating pad, comprising a heating unit consisting of a sheet of flexible material provided with an electrically conductive rubber composition to impart current conducting and heating properties to the sheet, electric conductor'wires secured along the sheet other so that current will be conducted across the area of the sheet lying between these wires to heat this area, and

covering material enclosing said unit.

8. A readily portable and flexible heating pad, comprising a heating unit consisting of a sheet of flexible material having applied thereto a plastic compound containing electrically conducting carbon black in amount sumcient to impart current conducting and heating properties to the sheet, electric conductor wires secured lying between along two edges of the sheet in parallel relation to each other so that current will be conducted from one wire to the other across the sheet to heat it uniformly, and covering material enclosing said unit.

9. A readily portable and flexible heating pad, comprising a plurality of heating units each consisting of a sheet of flexible material having applied thereto a plastic compound containing electrically conducting carbon black in amount across the area of the sheet lying between these parallel wires to heat this area uniformly, and covering material enclosing said unit.

11.A readily portable and flexible heating pad, comprising two heating units each consisting of a sheet of flexible material carrying sufficient electrically conducting carbon black to impart current conducting and heating properties to the ducted uniformly across the area of the sheet these parallel wires to heat this area. uniformly, switch controlled means for supplying current to either or both of said units, covering material enclosing said units, and an insulating sheet disposed between said units and having itsedges secured to said cover.

ARTHUR W. BULL. GLENN G. EAVENS. 

